As a visible light communication technique for transmitting information with images or moving images displayed on a display or the like, there is known a system that displays a specific two-dimensional code (QR code) in a part of a display image, picks up an image of the two-dimensional code with a camera of a cellular phone or the like, and receives information.
For example, Japanese Laid-Open Patent Application No. 2007-163233 describes a configuration for generating, when a car navigation system detects abnormality, failure diagnosis data including an abnormal signal indicating the abnormality, converting the failure diagnosis data into a symbol code (a barcode or a two-dimensional code) and displaying the symbol code on a display device, and allowing a user to visually recognize the failure diagnosis data by reading the displayed symbol code with a portable terminal device.
Japanese Laid-Open Patent Application No. 2006-020204 describes a configuration for reading a two-dimensional code printed on a display medium with a terminal device, accessing a server apparatus, which provides content such as images and sound, specified by the information of the read two-dimensional code, and acquiring various contents.
However, in the visible light communication techniques of the background art explained above, there is a problem in that, for example, when the two-dimensional code is displayed on a large display used in the street, the two-dimensional code spoils the appearance because the two-dimensional code occupies a part of an image (a public image) of an advertisement or the like displayed to the public.
As means for coping with such a problem, there is a so-called secure display technique in which a display device that displays, in a time division manner, a public image and an image provided to only specific users (a private image) and an optical shutter that transmits light in synchronization with display timing for the private image are combined.
In the secure display technique, a public image provided to unspecified people, a private image provided to only specific users, and a reverse image of the private image are displayed in a time division manner in one frame by the display device and the optical shutter present in front of the users is switched to a transmission state in synchronization with display timing for the private image. Consequently, only the private image is visually recognized by the users who use the optical shutter and only the public image is recognized by the unspecified people (public) who are present around the users and do not use the optical shutter because the private image is superimposed on the reverse image and changed to a half-tone (gray) image.
If the secure display technique is utilized, it is possible to provide, while providing the unspecified people with the public image, users, who use the optical shutter, with various kinds of information using the private image. Therefore, the appearance of the public image is not spoiled.
However, in the secure display technique, since the optical shutter is necessary to visually recognize the private image as explained above, users to whom the private image can be provided are limited. In general visible light communication, it is desirable that various kinds of information can be more easily provided to a large number of users by the private image.
For example, when an advertisement or the like is displayed by a public image and a URL (Uniform Resource Locator) of a server apparatus that provides, with a private image, detailed information of a commodity displayed by the public image, is displayed by a two-dimensional code or the like, convenience is low in a system that requires the optical shutter.
In the secure display technique, it is necessary to transmit a synchronization signal, which synchronizes with the display of the private image, from the display device to the optical shutter, to transmit only the private image displayed on the display device by the optical shutter and interrupt the public image and the reverse image.
However, in the visible light communication, when various kinds of information are acquired from an image displayed on, for example, a large display set in the distance, since users are not always in an environment in which the users can receive a synchronization signal, it is desired that it is possible to easily provide the users with the information without using the synchronization signal unlike the secure display technique.